1. Field of the Invention
The present invention relates to a joining method for a frame of spectacles, and in more particular to a joining method for a frame of spectacles by which a member (e.g. bridge and/or temple) is joined to another part (e.g. lens rim) of the frame of spectacles.
2. Description of the Prior Art
Shape memory alloy can have not less than two phases in a solid state, a phase stable at a high temperature is called austenite, and a phase stable at a low temperature is called martensite. And, a temperature at which a phase transformation occurs is called as a transformation temperature.
FIG. 1A illustrates a shape of a shape memory alloy at a temperature higher than a transformation temperature of the alloy. FIG. 1B illustrates the shape memory alloy of FIG. 1A is deformed longitudinally below the transformation temperature. FIG. 1C illustrates the shape memory alloy of FIG. 1A is deformed transversely below the transformation temperature. And, FIG. 1D illustrates a shape of the deformed shape memory alloy of FIGS. 1B or 1C at a temperature above the transformation temperature.
As depicted in FIGS. 1A, 1B and 1C, when the shape memory alloy having a specific shape above transformation temperature is deformed longitudinally or transversely below the transformation temperature, as depicted in FIG. 1D, the phase transformation occurs from martensite into austenite, accordingly the shape memory alloy returns to the original shape, herein the above-mentioned phenomenon is called shape memory effect.
NiTi alloy can have a shape memory effect of 8%, it means when the NiTi alloy having a length of 100 mm is deformed longitudinally so as to have a length not greater than 108 mm and is heated above the transformation temperature, the length of the NiTi alloy is returned to 100 mm.
In the meantime, in some materials, they are deformed by a certain loads without any temperature change and regain the original shape after removing the load, the above-mentioned phenomenon is called superelasticity effect. Accordingly, in a material having superelasticity effect, because a permanent deformation by an outer impact hardly occurs, it is possible to maintain the original shape always.
Shape memory alloy having the shape memory effect or the superelasticity effect can be used for a home appliance, an industrial appliance and a medical appliance, etc. In addition, with the development of a high-technology such as a computer and an information communication, etc., a miniaturization and an automatization technologies for a Ti—Ni group shape memory alloy actuator have been amazingly developed and put to practical use.
FIG. 2 schematically illustrates spectacles.
As depicted in FIG. 2, because a shape memory alloy is pleasant to the touch and is not deformed by an outer force, it is in the spotlight as a material for a frame of spectacles such as a bridge 4 or a temple 5, etc.
Generally, a NiTi alloy used for a frame of spectacles has a transformation temperature within a range of −20° C.˜0° C., it means it has the superelastricity effect at a temperature above 0° C.
However, because the NiTi alloy has a high reactivity on oxygen and nitrogen, etc., it is difficult to join directly the bridge 5 or the temple 4 made of the NiTi alloy to the lens rim 1 or the hinge 2 by spot welding.
Accordingly, in order to join the bridge 5 or the temple 4 to the lens rim 1 or the hinge 2, the end of the NiTi alloy bridge 5 is inserted into and joined to a pipe 3 having a good weldability and a small diameter, and the pipe 3 is joined to the lens rim 1 by the spot welding. In addition, the bridge 5 made of a NiTi material is connected to the hinge 2 by the pipe 3 having a small diameter.
In order to join a NiTi alloy material bridge or temple to a pipe, inserting a joining portion of the bridge or the temple into the pipe, compressing and deforming the pipe, namely, a clamping method can be used, but in the method, the joining portion may not come out but turn aside.
In addition, in order to join a temple, a method inserting a wire into a pipe and performing a brazing with hard solder can be used. However, a nickel plating, etc. has to be performed for the brazing. In addition, a temperature rise from the brazing may deteriorate the elasticity of NiTi shape memory alloy, and working surroundings may be deteriorated due to a poisonous gas occurrence, etc. in the brazing.